Generally, a drive controller is used for a drive control of a motor by the control of an electric current flowing in a motor, which is realized either by controlling an electric voltage applied to the motor, or by controlling an electric power supplied to the motor.
For example, a motor drive device disclosed in a patent document, Japanese Patent Laid-Open No. 2011-148379 (patent document 1) sets an electric current restriction level of a forced commutation to a higher-than-normal level, which is higher than a restriction level used in a motor rotation in a normal state at a constant number of motor rotations, when a position sensor-less type brushless motor is started, for a reduction of a start-up time.
Generally, a motor torque output from the motor is transmitted to a drive load via an engagement between a rotatable engager of a rotor and a force receiver of the load in a “rotatably-gapped state.”
More specifically, the rotatable engager is provided as a rod which engages with an inside of a hole of the force receiver for driving the load, or the rotatable engager is provided as a cylinder which engages with an outside of a rod of the force receiver for driving the load. In either case, at a drive start time or at a rotation reversed time, the rotatable engager engages with the force receiver after a small amount of rotation to collide with a wall of the force receiver, and after such a collision, the two parts start to rotate together.
When an operation immediately before such a collision of the rotatable engager with the force receiver is designated as a “collision preparation stage,” and an operation of the rotatable engager before the collision preparation state is designated as a “pre-operation state,” the transition from the pre-operation stage to the collision preparation stage is caused by a power supply switching.
For example, at the start time of the brushless motor of a position sensor-less type, the position of the rotor is “detected” by performing a preset power supply, and a drive start position is “determined” based on a detected position of the rotor, and the rotor is subsequently rotated to the drive start position by switching the power supply for the “positioning” of the rotor. In a three-phase brushless motor, two out of three-phases receive a power supply for a rotation of the rotor and a position of the rotor is detected based on an induction voltage in a non-power-supply phase, which is an operation in the “pre-operation stage,” and the rotation of the rotor to the drive start position for the positioning is performed in the “collision preparation stage.”
The collision of the rotatable engager with the force receiver, which may momentarily exceed a breakage threshold of the material of the two parts, or may be repeated to lead to a material fatigue, causes an abrasion or a breakage of weaker one of the rotatable engager and the force receiver, in combination of a complex external factors of high temperature, high pressure, strong vibration and the like.
For example, when the rod as the rotatable engager is made with metal and the force receiver is made with resin, the inner wall of the force receiver may be repeatedly collided with the rod at every start time, and may be fatigued, cracked, or broken.
In the device the of patent document 1, although the electric current restriction level is managed from a view point of reduction of a start-up time reduction of the brushless motor, no consideration is made for wear or breakage of the material caused by a collision between the rotatable engager and the force receiver or the like.